Ailtech 7600 Series Noise Generator ~ Operation and Service Manual, 11-1980.
ASHRAE Generator Noise Presentation · generator is due to the noise from the radiator fan, as will...
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Generator Noise Control - An Overview Introduction l Types of Generators l Generator Noise Sources l Noise Reduction Techniques l Case Study Return to www.enoisecontrol.com
Transcript of ASHRAE Generator Noise Presentation · generator is due to the noise from the radiator fan, as will...
Generator Noise Control - An Overview
Introduction
l Types of Generatorsl Generator Noise Sourcesl Noise Reduction Techniquesl Case Study
Return to www.enoisecontrol.com
o There are two categories of generators: Diesel andspark ignited. Spark ignited types include propane andnatural gas engines.
o The right hand graph on the next page shows the soundpower level difference between the two types ofstandard, unhoused generators. Y-axis is sound powerlevel, x-axis is sound pressure level. As can be seen inthe graph, the sound power level for natural gas andpropane are the same.
o Sound power level is similar to horsepower – it relates tothe total energy produced by the generator. Independentof distance or location.
o The left hand graph illustrates the variation of soundlevel with fuel type. This time the values are SoundPressure Levels, dBA. Sound Pressure Level varies withdistance and location from the source.
o For reference, the SPL of a quiet residentialneighborhood is 45 dBA during daytime hours, 35 dBA atnight. 100 feet from a busy freeway is 70 dBA. Normalconversation at 3 feet is 60 dBA.
ASHRAE TC 2.6
Generator Noise Control - An Overview
Types of Generators
o Dieselo Propaneo Natural Gas
Comparison of Generator Noise with Fuel Type
85.0
90.0
95.0
100.0
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110.0
115.0
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Octave Band Center Frequency, Hz.
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125 kW Diesel
125 kW Natural Gas
125 kW Propane
Sound Pressure Level by Engine Type, 7 m
86.0
84.1 84.1
70.0
75.0
80.0
85.0
90.0
125 kW Diesel 125 kW Natural Gas 125 kW Propane
Fuel Type
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Types of Generators
Comparison of Diesel Generator Noise with Size
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Octave Band Center Frequency, Hz.
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125 kW Diesel
500 kW Diesel
1 MW Diesel
2 MW Diesel
Sound Pressure Level by Engine Size, 7 m
86.0
91.0
94.0
99.2
70.0
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125 kW Diesel 500 kW Diesel 1 MW Diesel 2 MW Diesel
Size
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As expected, noise levels increase with size of generator.
Much of the additional low frequency noise associated with the 2 MWgenerator is due to the noise from the radiator fan, as will be shown in alater slide
ASHRAE TC 2.6
Generator Noise Control - An Overview
Generator Noise Sources
o Generator EngineBlock and AirIntake
This is the dominantsource of noise out theair intake openings intorooms containing agenerator.
ASHRAE TC 2.6
Generator Noise Control - An Overview
Primary Noise Sources
o Radiator FanRadiator fan noise combineswith the engine block to be thedominant sources of noiseradiating out of the discharge airopening in rooms containinggenerators.As we will see in the next slides,with larger engines the noisefrom the radiator fan candominate at least some portionsof the frequency spectrumproduced by the generator.
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Generator Noise Control - An Overview
Primary Noise Sources
o Exhausto Turbo Charger
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Generator Noise Control - An Overview
Primary Noise Sourceso Load Bank – 95 dBA @ 10 feeto Vibrationn Enginen Connections to ductwork, exhaust pipe,
electricalIn our experience load banks are often portable, brought in for occasional testing.They are very noisy. Many noise ordinances will allow portable equipment toexceed a code limit. If the load bank is not portable, or if the noise ordinancedoes not allow an exemption, it would need to be placed inside the generatorroom.Vibration is not normally a significant noise source, unless the generator islocated on an upper floor or roof. Spring vibration isolators are normally used toreduce the vibration to the supporting structure. Larger engines can damage thesupporting structure if vibration isolation is not provided.
ASHRAE TC 2.6
Generator Noise Control - An Overview
Primary Noise Sources2 MW Diesel Generator Sources
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Octave Band Center Frequency, Hz.
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Engine Block + Radiator
Engine Block, no Radiator
Exhaust Noise, no Muffler
2 MW Diesel Generator Sources
99.2
93.2
96.6
70.0
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Engine Block + Radiator Engine Block, no Radiator Exhaust Noise, no Muffler
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The significance of radiator fan noise is apparent in this slide,which shows engine sound levels with and without radiatorpresent. No exhaust noise is present unless noted.
ASHRAE TC 2.6
Generator Noise Control - An Overview
Noise Reduction Techniqueso Generator Roomsn Room Enclosureo Roofo Wallso Doorso Internal Lining
n Intake Air andDischarge Airo Duct Silencerso Acoustic Louverso Exterior Screens
ASHRAE TC 2.6
Generator Noise Control - An Overview
Noise Reduction Techniqueso Exhaust Noisen Resistive Mufflersn Active Noise Control
o Structure Borne Noise & Vibrationn Spring Isolators on Generators larger than 175
kW.n If floor joint is present, weight of concrete
beneath generator should be not less than twicethe generator weight.
n Flexible pipe connectors, duct connectors,electrical connection at generator.
ASHRAE TC 2.6
Resistive mufflers are available in at least three grades ofeffectiveness.
Industrial grade silencers reduce exhaust noise by 12-18 dBA.
Residential grade silencers reduce exhaust noise by 18-25dBA.
Critical grade silencers reduce exhaust noise by 25-35 dBA.
Active noise cancellation silencers used to be available as amanufactured product, but are not currently available. Theywere effective in reducing the low frequency tones associatedwith the cylinder firing.
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Generator Noise Control - An Overview
Case Studies
o 1000 kW Generator, housed inequipment room
o Direct Radiatoro Closest Receiver Property 50 feet
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Generator Noise Control - An Overview
Case Studyo 1000 kW Diesel Generatoro In generator room in lowest level of buildingo 50 feet to closest property
This shows plan view of generatorinside an enclosed room. This isthe most typical installation.Duct silencers are shown on intakeand discharge openings to room, ascreen is on the outside of theintake opening, and a muffler on theexhaust pipe. Acoustical louversare used sometimes instead of ductsilencers.
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Generator Noise Control - An Overview
Case Studyo Noise out of intake air opening to roomn Unhoused generator SPL at 50 feet, free field =
89 dBAn If generator is in a room, internal 4” thick lining
on two adjacent walls of room, with large inletlouvers close to the side of the generator asshown in previous slide, SPL at 50 feet = 88 dBA
n If low pressure loss silencers are added to inlet(static pressure drop = 0.10 at -1000 fpm), SPLat 50 feet = 73 dBA.
n If solid screen of sufficient size and mass isincluded outside of intake louvers, SPL at 50feet = 65 dBA.
ASHRAE TC 2.6
If the inlet louvers were substantially removed fromthe side of the generator, more reduction would beachieved by placing the generator in a room withacoustical absorption present.
In most cases, the size of the room is limited due tocost, and the outside air inlet louvers are very close tothe engine generator.
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Generator Noise Control - An Overview
Case Study
o Noise out of discharge air openingn Similar to intake opening.n Size of opening might be slightly less,
but radiator fan is closer to discharge.n Expected noise levels would be the
roughly the same as the intake – 89 dBAwithout room, 86 dBA with room, 73 dBAwith silencers, 65 dBA with additionalsolid screen.
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Generator Noise Control - An Overview
Case Study
o Exhaust Noisen In free field, at 50 feet, exhaust with no muffler
is 84 dBA, in direction of exhaust.n Point exhaust up, roughly 5 dBA attenuation, =
79 dBA at 50 feet.n Add Industrial Silencer, 15 dBA attenuation, 64
dBA at 50 feet.n Add Residential silencer instead, 22 dBA
attenuation on average, 57 dBA at 50 feet.n Add Critical grade silencer instead, 30 dBA
average attenuation, 49 dBA at 50 feet.
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Generator Noise Control - An Overview
Case Study
o Combine noise levels from varioussources.
o Inlet = 65 dBAo Discharge without screen = 73 dBAo Exhaust noise = 57 dBA with
residential grade silencero Combined level = 74 dBAo With screen on discharge, combined
level is 68 dBA.
ASHRAE TC 2.6
Generator Noise Control - An Overview Return to www.enoisecontrol.com
Case Studyo 68 dBA is higher than most ordinance limits for
residential use.o Even with these significant noise control measures,
required distance between generator room and closestresidential property would need to be approximately200 feet to reduce noise levels to 55 dBA.
o 55 dBA would be compatible with most noiseordinances at residential property.
o Another 20 dBA noise reduction in the room designcan be achieved with longer duct silencers andmultiple exhaust mufflers, but space requirements aresubstantial.
o Using remote generator radiators can further reducenoise levels from generator room.
ASHRAE TC 2.6
